1. Field of the Invention
This invention relates generally to fluorescent lighting apparatus; and particularly to apparatus and method improving assembly of leadless ballasts into fluorescent luminaires.
2. Prior Art
Ignition and maintenance of electrical discharges in fluorescent lamps generally require voltages much higher than ordinary line voltages, and in some instances heater circuits in such lamps also require specific lower voltages. Fluorescent light fixtures, known as "luminaires", accordingly have special transformer assemblies, "ballasts", for providing these specialized voltages.
Traditionally electrical connections at each ballast were provided in the form of relatively long wires extending from within the ballast. At the time of installation of the ballast into a luminaire, such wires in many instances were then connected with wire nuts to wires (provided by the luminaire manufacturer) running within the luminaire to electrodes and power terminals of the luminaire.
Such connections were time consuming and required some degree of special expertise--to make a good connection, as well as to complete the various circuits correctly. These awkwardnesses were particularly troublesome when ballasts required aftermarket replacement.
In other instances the ballast wires were long enough (usually just long enough) to connect directly to the electrodes and terminals. Such connections represented an improvement in that they were no more difficult than connecting the first-mentioned style of wiring into a luminaire--and one wiring step was thus eliminated.
Such ballasts with long wires, however, generally had to be made up specially for each luminaire type, introducing undesirable manufacturing inefficiencies and inventorying costs. Field replacement was also particularly onerous.
During the last few years, therefore, the fluorescent lighting industry has been turning to ballasts with no external leads--so-called "leadless ballasts". In such a ballast the leads terminate internally at a half-connector that is mounted in (or forms part of) the wall of the ballast case; this half-connector is most often aligned with (sometimes in the sense that it provides) an aperture in the wall.
For purposes of the present document, such a half-connector will be called an "internal" half-connector, as it is internal to the ballast case.
Upon installation of such a ballast into a luminaire, the wiring connections are most typically made by attaching a mating external half-connector that is wired to the luminaire electrodes and terminals. (Alternatively in some cases the luminaire wires are instead inserted individually into female terminals in the internal half-connector.)
Preferred designs make use of female half-connectors--often called "sockets" or "receptacles"--as the internal half, and male half-connectors or "plugs" for the external. One reason for this preference is the associated lower vulnerability to breakage of electrical equipment protruding from the ballast case during shipment and storage; however, the opposite design is also feasible, and the present invention is compatible with both.
Leadless-ballast configurations should be made reasonably safe in event of various sorts of adverse field conditions that stress the ballast-to-luminaire interface. For this purpose connectors are favored which incorporate latches to hold the two half-connectors together--even against considerable separating force, such as might arise for instance if a ballast were to fall out of a luminaire and hang by the wiring connections, or if inexperienced personnel were to tug strongly at the luminaire wires.
Generally the level of separating force which such a latch must withstand is considered to be twenty pounds. Many or most luminaire manufacturers now refuse to buy a leadless ballast that lacks a latch; and the latch-style connector is regarded as important to acceptance of leadless-ballast configurations not only by manufacturers but as well by testing laboratories that service the consumer-product industries.
The latch ordinarily takes the form of a hook-shaped retaining element, with an inclined-plane back portion that is used to deflect the hook during mutual engagement of the two half-connectors. This retaining element is resiliently mounted to one (usually the external one) of the half-connectors--most commonly by being formed in the material of that half-connector.
During assembly the hook is deflected by force applied against the inclined-plane back portion of the hook, and so moves in ratchet fashion past a retaining edge that is associated with the other half-connector. When this other half is the internal half-connector (as is usually the situation), for the sake of economy the retaining edge may be an edge of the aperture in the metal ballast-case wall; otherwise the retaining edge is supplied as part of the molded plastic half-connector body, adding significantly to the amount of plastic required.
After passing the retaining edge, the hook or like retaining element snaps resiliently into place behind that edge, providing the desired resistance against pull-out of the external half-connector. Notwithstanding such force, the side of the hook which now engages the retaining edge remains in engagement--because that side is not inclined--but whenever a user wishes to disconnect the ballast, the user can disengage the hook manually, by manually depressing the retaining element.
The use of mating half-connectors inside and outside the ballast case, despite the added cost of the connectors and additional procedures for wiring both halves, has been found very satisfactory--particularly as it greatly facilitates assembly (including field replacement), and confers substantial benefits of modularity in manufacture and inventorying.
Luminaire assembly work proceeds so much more quickly, however, that an unexpected ancillary difficulty arises. Some assembly-line workers have reported discomfort in their hands, seemingly arising from the repetitive work of forcibly inserting the external half-connectors into engagement with the internal half-connectors.
Some suggestion has been heard that such discomfort, and perhaps possibly eventual progressive disability, may arise from a phenomenon known in industry and elsewhere as "carpal tunnel syndrome". In any event, in practical terms this development is evidently associated with a repetitive wrist motion, under compression, needed to push the external half-connector into engagement.
During this motion the components tend to be essentially always in the same assembly-line position relative to the worker's stance. It appears that such effort could tire an operator on a longterm basis.
Such problems generally are incurred in the assembly facilities of luminaire manufacturers, representing a real and significant problem in some cases for the acceptability and hence the utility of lead less-ballast configurations. As can now be seen, important aspects of the technology in the field of the invention are amenable to useful refinement.